I am so sorry, and can understand your experience. It is very difficult. I spent many years working with animals at shelters. Only, no kill though. I then had an opportunity to work for the vet who treated our shelter animals for pay. All went ok, until one day she told me that she would be putting a dog down. The owners didn't have the money to pay. I offered to take the dog, illness and all. And was told that she had to honor the owners request. I had to leave the job. I didn't have any regrets.

I wish you well, it will be a challenge for you for sure. It takes a big heart to and gentle hands to do this much needed work.
Good luck.
warm regards,
Jade